The man page for "productbuild" for Mac OS talks about a distribution file:
--distribution dist-path Use the distribution file at dist-path to define the presentation, choices and packages to be installed by the product. Each of the package names referenced in the given distribution file must be found in a path specified with the --package-path flag.
But I can't find inforation about what goes in the distribution file anywhere. What sort of stuff goes in there? Is there a reference page for it?
It's certainly under-documented, but there is a little bit of information out there:
I'd also recommend examining distribution files inside existing packages. You can expand a flat package with: